It is well known in the art that adding a mixture of 4-10% recycled asphalt shingle by-product to road pavement enhances the pavement's stability, reduces cracking of the pavement, and increases the pavement's durability. Therefore, a demand exists for such by-products of recycled asphalt shingles and it is desirable to efficiently and economically grind asphalt shingles into byproduct for use in road pavement.
It has been previously known in the art to use wood-grinding apparatus to grind asphalt shingles. A wood grinding apparatus generally employs a large rotating drum with grinding heads attached to the outside of the drum. The drum is located inside an outer container having a screened portion. The screened portion allows wood chips to exit through the screen once they are small enough.
The wood grinding heads comprise a body for attachment to the outside of the rotating drum and a grinding tool that attaches to the body. As the drum rotates, the grinding heads also rotate and wood material is fed into the screened container and toward the rotating drum. As the material contacts the rotating grinding heads, the material is ground into by-product. This by-product continues to cycle around the inside of the screened container and be ground until the by-product's diameter is small enough to exit through the screened portion.
These wood-grinding apparatus work well grinding wood, but when grinding asphalt shingles they create excessive frictional heat that melts the shingles, thereby hindering the grinding and causing significant damage to the apparatus, as explained below.
A popular wood-grinding head used to process asphalt shingles is shown in FIG. 1. This figure illustrates sawtooth cutting heads 300 attached to the surface of the rotating drum 200. A number of cutting heads 300 are provided which are arranged axially and spaced circumferentially along the drum. Each cutting head 300 comprises a base 5 having a leading area 6 and a trailing area 7 (with reference to the direction of rotation R). A sawtooth cutting tool 43 is attached to the trailing area 7, while the leading area 6 acts as a raker. The raker 6 does not cut or grind but merely functions to gauge the depth at which the rear sawtooth cutting tool 43 cuts the material. For example, a cutting depth “x” is depicted in FIG. 1. During operation, the drum 200 rotates so that the leading area 6 of the cutting apparatus 300 travels ahead of the trailing area 7, thereby raking the material which is then cut by the sawtooth cutting tool 43. Thus, the shingle material is cut once each time it passes a cutting apparatus 300. As noted earlier, the process of raking and cutting with the sawtooth cutting apparatus 300 does eventually break down the asphalt shingles into a proper size, but not before friction creates excessive frictional heat.
The excessive heat is produced because the grinding apparatus inefficiently processes the extremely abrasive asphalt shingles. Most of the frictional heat is created when the raker of each head rubs against the shingles. Also, as the shingles must reach approximately one inch in diameter, they cycle around the inside of the screened container, thereby creating more friction. The shingles are cut and raked repeatedly until they are small enough to exit through the screen, thereby creating the excessive frictional heat that melts the shingles.
When the shingles melt inside the processing apparatus, the apparatus becomes bound and damages the drum-driving motor and the cutting heads. Also, the apparatus will not function again until the melted asphalt is removed, which is costly and time consuming. The available wood-grinders are too inefficient and create too much friction, thereby creating high temperatures that melt the asphalt shingles before the desired byproduct is produced.
The above noted problems are clearly evidenced by the fact that it was only commercially viable to use that apparatus to grind asphalt shingles in an extremely cold environment, such as the far northern hemisphere during winter, where extremely low temperatures prevented the shingles from melting during grinding. Thus, it would be desirable to develop a cutting apparatus and method for cutting asphalt shingles that produces the desired product while avoiding the inconveniences caused by melted shingles.